1. Field of the Invention
The present invention relates to a liquid pressure transfer printing method for a steering wheel rim of an automobile, and more particularly, to a liquid pressure transfer printing method for a steering wheel rim of an automobile in which a mask member used for accurately matching a boundary line and a transfer portion close to the boundary line in divisional transfer printing can be replaced by a polyvinyl alcohol layer of the transfer print film used for transfer printing, when a pattern is printed on the surface of a product formed of plastic, aluminum, steel, or wood and having an uneven 3-D shape, such as the structure of a steering wheel rim of an automobile, using a liquid pressure transfer printing method, so that subsequent steps can be omitted and productivity can be improved.
2. Description of the Related Art
In a typical and well known liquid transfer printing method, as shown in FIG. 1, a transfer printing film 4 floats on liquid 8a contained in a reservoir 8. An object subject to transfer printing, as shown in FIG. 2, is pressed onto the transfer print film 4 from the above, so that a pattern layer 4a of the transfer print film 4 is transferred to the surface of the object by the pressure of the liquid 8a. 
The transfer print film 4 includes a polyvinyl alcohol layer 4b (typically called a xe2x80x9cPVA filmxe2x80x9d) having a thickness of 25 through 30 xcexcm and the pattern layer 4a is formed by printed ink on one surface of the polyvinyl alcohol layer 4b. The thickness of the polyvinyl alcohol layer 4b is 3 through 5 xcexcm or less and actively dissolves in the liquid 8a. 
A steering wheel 2 of an automobile used as the object in the present invention includes a steering wheel rim (not referenced in FIG. 2) having a ring shape and formed of polypropylene, ABS (acrylotrile butadiene styrene copolymer) resin, or rigid expanded urethane, and a boss portion (not referenced in FIG. 2) integrally coupled to the steering wheel rim (including divisional transfer printing portions a and b). The outside of the boss portion is molded by soft urethane, or is coated with leather according to types of products.
In the structure of the above steering wheel rim 2, a liquid pressure transfer printing process is performed to an exposed surface of the steering wheel rim corresponding to a portion other than a portion connected to the boss portion, that is, the divisional transfer printing portions a and b. The surface of the boss portion corresponds to a non-transfer portion 1.
Well-known technologies concerning a method for transfer printing using the transfer print film 4 with respect to the above steering wheel rim are disclosed in Korean Patent Application Nos. 98-17424, 98-17425, 98-36990, 98-36991, and 99-3368 which were filed by the present applicant.
Korean Patent Application No. 98-17424 discloses an invention to solve a problem such as extension and deformation of a print pattern or mismatch in a print state occurring in the conventional liquid pressure transfer print method in which the transfer print film 4 floats on liquid and a steering wheel rim is pressed from above to transfer the print. A selective transfer print is possible with respect to part of a surface or the entire surface b using a mask member 3 (refer to FIG. 3), such as a masking tape or rubber jig. Thus, with respect to the steering wheel rim 2, such as a ball or a circular ring on which transfer printing is difficult, a high quality match is maintained and, simultaneously, a plurality of patterns or shapes can be realized on the object.
FIG. 3 shows steps of liquid pressure transfer print in order according to the invention disclosed in Korean Patent Application No. 98-17424, in which a masking tape and PVA solution are used as a mask member 3 and a protective film 14, respectively.
The transfer print film 4 floats on the liquid 8a. To primarily perform transfer printing on a divisional transfer print portion b at the lower side, the mask member 3 is attached to an upper divisional transfer print portion a (in the first step). The steering wheel rim is lowered so that a transfer print surface 5 is formed (in the second step). Here, the pattern layer 4a reacts with a solvent on the steering wheel rim and completely adheres to the rim surface. Since the polyvinyl alcohol layer 4b remains, the remaining polyvinyl alcohol layer is washed and removed, and then dried. Next, PVA solution is applied to the dried transfer surface 5 to form the protective film 14 (in the third step) and the protective film 14 is dried. The mark member 3 covering the upper divisional transfer print portion a is removed (in the fourth step) so that a second transfer print surface 5a that is clean and to which transfer printing has not yet been performed is exposed. The second transfer print 5a is flipped to face downward and liquid pressure transfer printing is performed in the same manner as in the first transfer printing (in the fifth step). Here, the pattern layer 4a is partially transfer printed to the surface of the protective film 14 over a boundary 6 of the protective film 14. Since the protective film 14 is soluble, the protective film 14 is removed together with an overlapped transfer print portion during the subsequent cleaning step. Thus, a finished product having the transfer print surface 5 in which the transfer-printed patterns are matched at the boundary line 6, can be obtained (in the sixth step).
However, in the liquid pressure transfer printing method, when an end portion of the boundary of the mask member 3 makes an angle of 60xc2x0 or less with respect to the steering wheel rim, as shown in FIG. 4, the first and second transfer print films 4 closely adhere to the surface of the steering wheel rim so that no air bubble is interposed therebetween (refer to FIG. 5) during the first and second transfer prints and the transfer-printed patterns are matched and naturally connected at the boundary. Thus, a highly precise step of cutting the thin mask member 3 at an angle of 60xc2x0 or less is needed. Also, when the mask member 3 covering the divisional transfer print portion a is removed in the state in which the protective film 14 is applied to the first transfer print surface 5 and dried, the boundary portion of the protective film 14 partially overlapped on the surface of the mask member 3 may be irregularly removed, thus-causing mismatching of patterns.
The invention disclosed in Korean Patent Application No. 99-3368 concerns faster and accurate matching of patterns by reducing the difficulty in working the abovedescribed invention in which precision is required with respect to matching of the print pattern at a boundary portion of the mask member. This invention suggests a solution to problems of maintaining the inclined angle of the end portion of the mask portion at 60xc2x0 and accurately attaching the mask member after continuous transfer prints to maintain a distance of 0.1-0.2 mm from the center line.
However, the above liquid pressure transfer print methods, in which two cleaning steps and the protective film of a PVA solution are used, generate a large amount of waste water, which causes another problem of contaminating the environment.
Korean Patent Application Nos. 98-17425, 98-36990, and 98-36991 disclose a variety of inventions enabling mass production by adopting the liquid pressure transfer print method suggested by the invention of Korean Patent Application No. 98-17424.
The above liquid pressure transfer print methods include a sequence of steps using a mask member which is similar to the above-described steps, but different in that a masking tape (mask member) is used instead of using PVA solution as a protective film of the first transfer print surface. Thus, since a mask member that is not dissolved in solution is used in masking the first transfer print surface, accurate matching of a boundary line with the mask member attached to the second transfer print surface is needed. To perform such work consumes much time and reduces productivity.
To solve the above-described problems, it is an object of the present invention to provide a liquid pressure transfer printing method for a steering wheel rim of an automobile in which a mask member used for accurate match of a boundary line and transfer print portions adjacent thereto is replaced by a polyvinyl alcohol layer of a transfer print film used for transfer print in the step of divisional transfer print when a predetermined pattern layer is to be transfer printed b using a liquid pressure transfer print method using a transfer print film onto a surface of a product having a very uneven 3-D shape, so that a plurality of subsequent steps can be omitted, thus remarkably improving productivity, one time cleaning step minimizes the amount of waste water generated so that environment pollution can be reduced.
To achieve the above object, there is provided a liquid pressure transfer print method for a steering wheel rim of an automobile by which a predetermined pattern is transfer printed on one side surface of the steering wheel rim divided into two side surfaces in a lengthwise direction by using a transfer film in which a pattern layer is formed on a polyvinyl alcohol layer. The method comprises lowering the steering wheel rim for a predetermined time, to a boundary line of a primary transfer print portion, without attaching an additional mask member to the other side surface of the steering wheel rim opposite to the primary transfer print portion, after floating the transfer print film on liquid (a first transfer print step). Half drying the polyvinyl alcohol layer coating the primary transfer print portion of the steering wheel rim in the first transfer print step, for a predetermined time and at a predetermined rate (a half drying step). When the polyvinyl alcohol layer at the outer side of a first transfer print surface in the half drying step is dried to a gel state, flipping the steering wheel rim and lowering the other side surface to be transfer printed over the boundary line for a predetermined time (a second transfer print step), and soaking the steering wheel rim having the entire surface thereof completely transfer printed in solution for a predetermined time and cleaning the outside polyvinyl alcohol layers of the first and second transfer print surfaces by injecting the solution against the surface of the steering wheel rim for a predetermined time (an entire surface cleaning step)
It is preferred in the present invention that the steering wheel rim is dipped to be inclined at a predetermined dipping angle so that air bubbles are prevented from entering between the pattern layer of the transfer print film and the steering wheel rim during the first and second transfer print steps and the steering wheel rim is continuously dipped in a horizontal state, and that the dipping angle of the steering wheel rim is maintained between 1-5xc2x0.
It is preferred in the present invention that the time for transfer print in the first and second transfer print steps is 7-14 seconds.
It is preferred in the present invention that the half drying step is performed by having the transfer surface face downward, and that, in the half drying step, the polyvinyl alcohol layer is naturally dried by being exposed to the air at the normal temperature for 30-90 minutes.
It is preferred in the present invention that, in the half drying step, the polyvinyl alcohol layer is forcedly dried by being heated at a temperature between 60-90xc2x0 C. in a closed space.
It is preferred in the present invention that, in the half drying step, the drying rate of the polyvinyl alcohol layer is maintained between 60-70%.
It is preferred in the present invention that, in the entire surface cleaning step, the steering wheel rim is dipped in the solution at a temperature of 30xc2x0 C. for 50-90 seconds and a solution injection apparatus injects the solution for 10-12 minutes to completely removed the polyvinyl alcohol layer remaining after a dipping process.